Current methods of placement and positioning of coils for Transcranial Magnetic Stimulation (TMS) studies are either manual methods or approaches designed for research that require expensive and complex imaging or computational systems to determine three dimensional spatial coordinates for positioning reference. These techniques have severe clinical limitations. The manual methods do not provide a convenient means for repeated and accurate placement, while the three dimensional spatial methods based on imaging modalities are expensive, time consuming, and not conducive to clinical use. Accordingly, the present assignee has developed a positioning technique for clinical use that provides a simple way for the operator to perform repeated and accurate coil placement for TMS studies and treatments in a time-efficient and inexpensive manner. This TMS coil positioning technique is described in U.S. patent application Ser. No. 10/752,164, filed on Jan. 6, 2004, the contents of which are incorporated herein by reference.
Further techniques are also needed to comfortably hold the coil in place at the treatment position throughout a therapy session. Close approximation of the TMS stimulation coil to the patient's head during location of the motor threshold position or during therapy applications is critical to ensure that the proper magnetic field intensity is applied to the patient. The coil must remain in contact with the scalp throughout the application of stimulation pulses. The clinician does not currently have a good method to ensure that the coil is in contact, and has no means of feedback as to whether the coil has moved away from the scalp during treatment. If the coil movement occurs during the motor threshold (MT) level determination procedure, an inappropriately high power setting may be used. On the other hand, if the movement occurs after MT determination and during the treatment session, an inappropriately low magnetic field may be applied to the patient resulting in possibly reduced efficacy.
Current methods of holding the TMS coil against the patient's head include holding it by hand throughout the TMS procedure, supporting it with a mechanical arm and relying on the patient to remain still relative to the coil throughout the procedure, and mechanical alignment methods (e.g. Brainsight™ system) that physically restrain the patient's head against the coil. However, such solutions do not ensure that the coil is initially positioned against the patient's head or that the coil stays against the head throughout the procedure. These methods rely on the clinician to visually observe that contact is being made. Such observations may not be reliably be made continuously throughout the procedure. In addition, there are no solutions that provide feedback to the operator as to the state of coil contact.
Many companies provide pressure and contact sensors, including for medical applications (e.g. Tekscan), but these sensors are not designed for optimal use in the unique environment of a pulsed high magnetic field or for TMS use, and the present inventors are not aware that such sensors have been used to assist the clinician in maintaining TMS coil contact with a subject's head throughout treatment. Accordingly, an apparatus and technique for detecting that a TMS coil is and remains in contact with the patient throughout the TMS therapy procedure is needed. The present invention addresses this need in the art.